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United States Patent |
5,294,585
|
Moreau
,   et al.
|
March 15, 1994
|
Preparation of particulate composite material with carbon matrix
Abstract
The present invention concerns a polyphase particulate composite material
containing a microporous phase which is essentially carbon whose
microporous volume is between 0.1 cm.sup.3 /g and 1 cm.sup.3 /g, which is
associated with an amorphous mineral dispersed phase essentially
consisting of an oxide of silicon, aluminum, titanium or magnesium
disposed on the carbon phase, at a thickness of less than 10 nm. The
invention is also concerned with a process for the preparation of these
composite materials, and the use thereof as a molecular sieve.
Inventors:
|
Moreau; Serge (Velizy Villacoublay, FR);
Sardan; Bernard (Le Chesnay, FR);
Ehrburger; Pierre (Didenheim, FR)
|
Assignee:
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L'Air Liquide, Societe Anonyme Pour l'Etude et l'Exploitation des (Paris, FR)
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Appl. No.:
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725469 |
Filed:
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July 3, 1991 |
Foreign Application Priority Data
Current U.S. Class: |
502/413; 95/130; 95/138; 502/182; 502/415; 502/417 |
Intern'l Class: |
B01J 020/10; B01J 020/08; B01J 020/04; B01J 020/20 |
Field of Search: |
502/413,415,417,182
|
References Cited
U.S. Patent Documents
4125482 | Nov., 1978 | Sinha | 502/417.
|
4178270 | Dec., 1979 | Fujita et al. | 502/182.
|
5051389 | Sep., 1981 | Lang et al. | 502/182.
|
Foreign Patent Documents |
0107494 | May., 1984 | EP.
| |
0119924 | Sep., 1984 | EP.
| |
375658 | May., 1923 | DE2.
| |
55-51436 | Apr., 1980 | JP.
| |
61-212309 | Sep., 1986 | JP.
| |
2075357 | Nov., 1981 | GB | 502/182.
|
Other References
Anonymous, "Type CAL Granular Carbon," Calgon Corporation, Aug. 1986, pp.
23-105e et seq.
Chemical Abstract, vol. 93, No. 8, p. 177, Abstract No. 74869g.
|
Primary Examiner: Konopka; Paul E.
Attorney, Agent or Firm: Oliff & Berridge
Claims
We claim:
1. Process for the preparation of composite particulate material, which
comprises contacting an essentially carbon microporous particulate matrix
with a volatile gaseous precursor, said precursor comprising silicon,
aluminum, titanium or magnesium, and heat treating the matrix to decompose
the precursor on the matrix in situ at the temperature of decomposition of
the volatile precursor and form said material, wherein said material
includes an essentially carbon microporous phase having a microporous
volume between 0.1 and 1 cm.sup.3 /g, associated with an amorphous mineral
dispersed phase essentially containing a mineral oxide selected from the
group consisting of silicon, aluminum, titanium and magnesium oxides,
disposed on the carbon phase to a thickness of less than 10 nm.
2. Process according to claim 1, wherein the contacting and the
decomposition are simultaneous.
3. Process according to claim 1, further comprising, prior to said
contacting, pretreating the matrix by heating under vacuum or by flushing
with a neutral gas.
4. Process according to claim 1, further comprising post-heat treating the
matrix with a neutral gas or under vacuum at the temperature of the
decomposition of residual precursor materials.
5. Process according to claim 4, further comprising, after decomposition of
residual precursor materials, carrying out on the matrix a supplemental
heat-treatment to modify the microporous volume of said composite.
6. Process according to claim 1, wherein the precursor is a salt of an acid
or an alkoxide of silicon, aluminum, titanium or magnesium.
7. Process according to claim 6, wherein said precursor consists of
tetraethoxysilane.
Description
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention concerns particulate composite materials with carbon
matrix, a process for the preparation of these composite materials and
their application for the separation of molecules, such as for the
adsorption of gases.
(b) Description of Prior Art
It is known, in the field of molecular separation and adsorption, to use
activated carbon, i.e. porous carbon supports. One way to control the
porosity consists in providing a carbon deposit on a carbon support, for
example by pyrolysis or cracking, in general after heat activation.
These adsorbents have however the disadvantage of being essentially carbon
and for this reason are sensitive to oxygen from the air and to polluting
agents which, by adsorption, modify the characteristics of porosity and
therefore of adsorption.
SUMMARY OF THE INVENTION
A particulate composite polyphase material has now been found which
contains an essentially carbon microporous phase whose microporous volume
is between 0.1 cm.sup.3 /g and 1 cm.sup.3 /g, which is associated with an
amorphous mineral dispersed phase essentially consisting of a mineral
oxide selected from the oxides of silicon, aluminum, titanium or
magnesium, disposed on the carbonated phase, at a thickness of less than
10 nm.
The composite materials according to the invention, are less sensitive than
carbon sieves, in particular while in contact with oxygen and organic
polluting agents; and, quite a noticeable differentiation between oxygen
and nitrogen has been observed.
An object of the present invention is to provide a process for the
preparation of a polyphase composite particulate material, characterized
in that an essentially carbon microporous particulate material is
contacted with a precursor of a mineral oxide of the type comprising an
oxide of silicon, aluminum, titanium or magnesium, and in that the matrix
is heat treated to decompose the precursor in situ at the temperature of
decomposition of the precursor on the matrix.
The carbon matrix according to the invention or which can be used in the
process, may include activated carbon of plant origin, such as carbon from
coconut, pine bark or charcoal, or of mineral origin, such as coal or
anthracite, and more generally any non-crystalline carbon matrix having a
porous structure.
The carbon matrix may be pre-treated in order to control its porosity for
example by oxidation with oxygen, or water vapour or carbon dioxide, as is
the case for activated carbon.
Notwithstanding its origin and the possible pre-treatments made on the
matrix, the porosity of the latter is preferably between 0.1 cm.sup.3 /g
and 1 cm.sup.3 /g.
The mineral oxides which constitute the dispersed phase may be selected
among the oxides of silicon, aluminum, titanium or magnesium; and they are
advantageously present in the composite material in an amount of 0.1 to
10% by weight, preferably from 0.5 to 5.5% by weight, at a thickness lower
than 3 nm, preferably between 0.1 and 3 nm.
The amorphous dispersed phase modifies the porous structure of the entire
carbon matrix on which it is disposed and as a result, it modifies the
adsorption sites on and among the latter. With the oxide of silicon in the
form of amorphous silica, excellent results are obtained.
The proportion of oxide incorporated into the matrix depends on the size
and characteristics of adsorption of the molecules which are separated and
the characteristics of the carbon matrix.
In order to separate the molecules by molecular screening, the size of the
particles of composite material is between 0.5 and 5 mm.
The particles of the composite material may be obtained, either from the
screened starting material, or from crushed material, screened and then
agglomerated with a binder.
This process consists of contacting the matrix and the precursor of oxide
and treating the mixture to decompose the precursor on the matrix and
providing a deposit on the internal surface of the matrix. The
decomposition temperature may be favorably comprised of between
350.degree. and 650.degree. C., preferably between 500.degree. and
550.degree. C.
The oxide precursor may include any volatile organic compound which can be
cracked containing silicon, magnesium, titanium or aluminum, such as
alkoxides or acid salts, as well as any volatile compound which, by
decomposition under heat, gives a stable inorganic residue. As preferred
alkoxides, the methoxy, ethoxy and propoxy derivatives may be mentioned.
The preferred salts of acid are chlorides and bromides. In particular,
compounds of the type aluminum ethoxide may be used as a precursor of
aluminum oxide, as precursor of silica tetraethoxysilane may be used, and
as precursor of titanium oxide, titanium(IV)isopropoxide may be used.
It may be advantageous to pre-treat the carbon matrix in order to desorb
the chemical species which are adsorbed by the matrix, such as oxygen.
This pre-treatment may take place under vacuum or in a gas which is
chemically inert towards carbon, and at temperatures which are compatible
with the matrix, i.e. lower than 1300.degree. C., for example of the order
of 500.degree. C. to 1000.degree. C.
Contact of the matrix with the precursor may be carried out while the
precursor is in gaseous phase, by adsorption of the precursor by the
matrix. This contact may be carried out under a pressure which corresponds
to the vapor pressure of the precursor, by means of consecutive steps or
continuously. It may also be carried out under a higher pressure, the
partial pressure of the precursor remaining the vapor pressure of the
precursor while in the presence of an inert gas carrying a gaseous
precursor. The contact of the matrix with the precursor may also be
carried out by liquid injection in a sealed enclosure. Under these
conditions, the decomposition of the precursor and the deposit are carried
out under pressures higher than the vapor pressure of the precursor. The
influence of the presence of the reaction products is here completely
different than that of the deposits under a saturating pressure.
The annexed FIGS. 5 and 6 illustrate variations of the kinetic conditions.
Adsorption may take place at room temperature or at a temperature lower
than that of the heat treatment.
The heat treatment which follows enables the decomposition of the precursor
and the deposit of the oxide in situ, on the entire internal surface of
the matrix.
The adsorption and the heat treatment may also be carried out
simultaneously.
In the particular case of tetraethoxysilane, which is a precursor of
silicon, the decomposition temperature is about 600.degree. C.
Once the deposit has been produced, it may be advantageous to remove the
residual amounts of the precursor remaining in the matrix from the
composite material, by means of a post heat treatment under vacuum or by
flushing a neutral gas, at a temperature which is compatible with the
stability of the matrix, i.e. lower than about 1300.degree. C., for
example between 500.degree. C. and 1000.degree. C.
For example, nitrogen or argon are used as a carrier gas when contacting
the oxide precursor and the matrix, or as chemically inert gas towards
carbon or in both cases.
The composite materials according to the invention, i.e. the carbon
materials in which the adsorption sites are modified by deposits of
mineral oxides have determined the properties of adsorption of molecules.
A controlled deposit enables one to make materials specific with respect
to certain molecules and to make them useful in selective adsorption.
Consequently, the new composite materials find application in the
separation of molecules by molecular screening. In particular, they may
advantageously be used for the separation of gases, such as gases from
air, for example nitrogen, oxygen and argon.
The technique of adsorption by pressure variation (PSA, Pressure Swing
Adsorption) may be applied with these composite materials when used as
adsorbent for the separation of gases.
BRIEF DESCRIPTION OF DRAWINGS
The annexed drawings represent the volume of gases from the air which have
been adsorbed (+ Nitrogen, * Oxygen, Argon Ncm.sup.3 /g of adsorbent,
ordinate) as a function of time(s) (abscissa).
FIG. 1 is a comparative figure, for an activated carbon based on calcined
coconut by treatment at 950.degree. C. during four hours under argon, then
at 950.degree. C. during three hours under vacuum;
FIG. 2 is a similar view for the same calcined coconut by pre-treatment at
950.degree. C. during four hours, then treatment with tetraethoxysilane
under saturating vapor pressure, resulting in a deposit of 1.3% by weight
of silica, then a post-treatment during 8 h at 950.degree. C.;
FIG. 3 is a similar view for the same coconut calcined by pre-treatment at
950.degree. C. during 4 hours, then treatment with tetraethoxysilane with
a deposit of 0.7% SiO.sub.2, then post-treatment at 950.degree. C. during
8 hours;
FIG. 4 is a comparative view, for activated carbon based on charcoal of the
type activated carbon 2/10 BK R of CECA pre-treated, heated twice under
vacuum at 950.degree. C. during 4 hours;
FIG. 5 is a similar view for the same activated carbon, pre-treated
similarly as at 4, including an injection of tetraethoxysilane on 170 mg
of carbon in sealed capsule, followed by heating at 550.degree. C. during
one day;
FIG. 6 is a similar view for the same activated carbon, pre-treated in the
same manner and with a different injection of tetraethoxysilane in sealed
capsule, followed by heating at 550.degree. C. during one and a half day.
The deposits have been made under pressure, the treatment was carried out
at 550.degree. C. in sealed capsule under an atmosphere of argon. The
residues have been removed by a post-heat treatment under vacuum at
950.degree. C. during 4 hours.
In the case where the final composite material would present a porosity
which is too tight by reason of an excess of tetraethoxysilane, it is
possible to provide a subsequent oxidizing treatment, with water vapor,
oxygen or carbon dioxide, to give the desired porosity.
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